There are some articles about this here:
ABC News: Rare Germ Found in D.C., but No Terror Fears
Airborne Bacteria May Have Been In Air Over DC, CDC Says
As a biologist, I notice and remember odd things, and I did see a dead rat on the capitol mall, apparently well-fed and uninjured, otherwise healthy looking, and fresh enough not to be visibly decaying, but old enough, or smelly enough, to have attracked a bot fly that was checking it out, crawling over its soft gray fur. It was on the steps leading to one of the Smithsonian Museums. I didn't pick it up or look at it too closely, because I am not stupid (in that way). I pantomimed that I was going to eat it, so I was able to confirm this memory with someone else that was there. I forgot to ask when exactly they remembered this, but I am pretty sure it was at the end of the march. Probably just a coincidence. However, if I were responsible for public health in a city like D.C., I would have a freezer full of dead rats like this (and rabbits, squirrels, etc.) and have systematic collection and reporting of them by city maintenance personnel.
Anyway, I think this event and its timing is really odd, and it is a reminder that our government (for those of in the U.S.) has never fully explained the anthrax attacks that happened around 9/11.
For what it is worth, I have done careful literature reviews in the past on zoonotic diseases associated with U.S. rodents, including tularemia, and participated in formal laboratory research on Lyme disease. Having been there that day, and knowing what I know, I think it is irresponsible that the government is not treating this as a probable biowarfare attack.
It is also entirely possible that one or more dead rats like I saw there, were run over by lawnmowers and turned into aerosols, in the hours before the march.
Anyone who was there that got sick after the march,or gets sick, should take this seriously :)